SpaceX is set to announce the first private passenger to fly around the Moon on one of its spacecraft, the company tweeted Thursday.

"SpaceX has signed the world’s first private passenger to fly around the Moon aboard our BFR launch vehicle—an important step toward enabling access for everyday people who dream of traveling to space," the Elon Musk-led company wrote in a tweet. "Find out who’s flying and why on Monday, September 17."

SpaceX has signed the world’s first private passenger to fly around the Moon aboard our BFR launch vehicle—an important step toward enabling access for everyday people who dream of traveling to space. Find out who’s flying and why on Monday, September 17.

On Twitter, Elon Musk was asked who the passenger is and simply responded with an emoji of the Japanese flag. Speculation swirled following the tweet, leading some to believe it might be SoftBank CEO Masayoshi Son.

In 2017, Japanese internet conglomerate SofBbank, which runs the $93 billion SoftBank Vision Fund, invested in satellite broadband provider OneWeb, a business which SpaceX is also interested in, according to leaked documents obtained by Quartz.

History of space tourism

Despite the excitement surrounding the announcement, spacetourism has happened before.

In 2009, space tourist Guy Laliberté flew to the International Space Station aboard the Soyuz TMA-16, leaving from Kazakhstan. Laliberté was the seventh and last space tourist, prior to SpaceX's announcement on Monday.

Other non-astronauts that have flown into space include inventor Gregory Olsen, and multimillionaire Dennis Tito, the first tourist in space, after he paid $20 million to spend 8 days on the ISS in April 2001.

Virgin Galactic, founded by Richard Branson, is also working on developing commercial spacecraft to provide "suborbital spaceflights to space tourists," according to its website. And Jeff Bezos, the founder of Amazon, is also working with his company, Blue Origin, on getting tourists to space.

SpaceX's BFR

The BFR (also known as the Big Falcon Rocket) is SpaceX's upcoming two-stage reusable spaceship system that will weigh 9.7 million pounds and be capable of taking a 330,000 pound payload to Mars and lower-Earth orbit (LEO). The BFR, announced in September 2017, will eventually replace SpaceX's other launch vehicles, the Falcon 9 and Falcon Heavy, as well as its Dragon spacecraft.

In April, Musk posted a picture to Instagram (since removed) of what he described as the “main body tool” for his company’s BFR interplanetary spaceship.

In an interview in March, Musk said the ship was currently being built, adding "I think we'll probably be able to do short flights, short sort of up-and-down flights, probably sometime in the first half of next year."

Shortly after his successful Falcon Heavy Launch, Musk said he expected a “full-scale test” of the massive rocket within the next few years.

Musk described a slightly scaled-down 348-foot-tall rocket in September 2017 and announced that the private space company aimed to launch two cargo missions to Mars in 2022. He called the goals at the time “aspirational.”

Two more cargo missions would follow in 2024 to provide more construction materials, along with two crewed flights, according to earlier reports. The window for launching to Mars occurs every two years.